1. Field of the Invention
This invention relates generally to helical coil fasteners for securing insulation or other material to a roof deck. More particularly, the invention is directed to helical coil fasteners for securing insulation material to a tectum or to a light gauge metal roof deck.
2. Description of the Prior Art
Roofs are made of various materials with appropriate fasteners to secure insulation to the upper surface of a roof deck. Some roof decks are made of metal sheets, and others are made of a composite pressed fibrous material called tectum which offers relatively little resistance to the pull-out of conventional screws used to attach insulation to a tectum. The insulation in turn is normally covered with a single ply plastic material.
Attempts have been made to overcome the problem of pull-out by using screws with large diameters and providing a deep thread which contacts the tectum, but the large screws are not completely satisfactory. Such screws cannot be made by normal heading equipment and they require special tools for insulation. The INSUL-FIXX plastic stress plate and screws manufactured and sold by Townsend Division of Textron Inc. and disclosed in U.S. Pat. No. 4,361,997, which is owned by the assignee of the instant application, is excellent for securing insulation to sheet metal roof decks but is not as effective with tectum and other materials of similar strength.